Light emitting diodes (LEDs) emitting white light are next-generation light emitting device candidates which can replace fluorescent lights as the most representative conventional lights.
Light emitting diodes have low power consumption as compared to conventional light sources and are environmentally friendly because they do not contain mercury, unlike fluorescent lights. In addition, light emitting diodes have advantages of long lifespan and high response speed as compared to conventional light sources.
Such an LED may be used in combination with a phosphor which absorbs light emitted from the LED and emits various colors of light. The phosphor generally emits white, green and red light.
Oxide-based phosphors which emit light based on rare earth elements have been known and some oxide-based phosphors are commercially available. However, unlike phosphors, which have been conventionally used for CCFLs for PDPs, CRTs and LCDs, phosphors for LEDs need to efficiently emit light, based on excitation from ultraviolet to blue light.
Many nitride phosphors or oxy-nitride phosphors which satisfy this requirement are present, but a research on these phosphors is not actively performed. Oxy-nitride phosphors of M-Al—Si—O—N and M-Si—O—N (M: alkali earth metal) are known. As reported in Patent Document 1 (Japanese Patent Laid-open Publication No. 4415547) and Patent Document 2 (Japanese Patent Laid-open Publication No. 4415548), M-Si—O—N includes two types of alkali earth metal elements, thereby obtaining phosphors having an orthorhombic crystal structure.
However, the oxy-nitride phosphors have lower brightness than currently commercially available oxide phosphors. Accordingly, oxy-nitride phosphors require improved brightness for commercialization.